/a /b pstack
pop   pstack
mark  exch pstack
dup   pstack
clear
/x /y /z 2 copy pstack
pop pop  1 copy pstack
pop      0 copy pstack
2         index pstack
clear
/x /y /z  0 index ==
/x /y /z  1 index ==
/x /y /z  2 index ==
clear
/p /q /r  3 -1 roll pstack
3  1 roll pstack
count ==
mark 4 1 roll
counttomark ==
/A 5 1 roll
cleartomark
pstack
{ (a) (b) (c) -1 3 roll } stopped {
    _errorname ==
} {
    (RANGECHECK error is expected but got NONE) ==
} ifelse
clear
